Astronomers Spot Bright New Object near Cygnus A Galaxy’s … – Sci-News.com

Pointing the Karl G. Jansky Very Large Array (VLA) at the well-known and often-studied galaxy Cygnus A for the first time in more than 20 years, astronomers got a big surprise, finding that a new object had appeared near the galaxys supermassive black hole.

Artists conception of the newly-discovered object orbiting the main, central supermassive black hole of the galaxy Cygnus A. Image credit: Bill Saxton / NRAO / AUI / NSF.

Cygnus A, also known as LEDA 63932, NRAO 620 and IRAS 19577+4035, was discovered by radio-astronomy pioneer Grote Reber in 1939.

Located 800 million light-years away in the constellation Cygnus, the galaxy is one of the strongest radio sources in the sky.

Cygnus A was an early target of the VLA after its completion in the early 1980s. Detailed images from the VLA published in 1984 produced major advances in scientists understanding of the superfast jets of subatomic particles propelled into intergalactic space by the gravitational energy of supermassive black holes at the cores of galaxies.

The VLA images of Cygnus A from the 1980s marked the state of the observational capability at that time, said National Radio Astronomy Observatory astronomer Dr. Rick Perley, one of the researchers who made the original Cygnus A observations with the VLA in the 1980s.

Because of that, we didnt look at Cygnus A again until 1996, when new VLA electronics had provided a new range of radio frequencies for our observations. The new object does not appear in the images made then.

However, the VLAs upgrade that was completed in 2012 made it a much more powerful telescope, so we wanted to have a look at Cygnus A using the VLAs new capabilities.

The new object may have much to tell us about the history of this galaxy, said Dr. Daniel Perley, an astronomer with the Astrophysics Research Institute at Liverpool John Moores University and Dr. Rick Perleys son.

The researchers began the new observations in 2015, and continued them in 2016.

To our surprise, we found a prominent new feature near the galaxys nucleus that did not appear in any previous published images, Dr. Rick Perley said.

This new feature is bright enough that we definitely would have seen it in the earlier images if nothing had changed. That means it must have turned on sometime between 1996 and now.

The team then observed Cygnus A with the Very Long Baseline Array in November of 2016, clearly detecting the new object.

What is the new object? Based on its characteristics, the astronomers concluded it must be either a supernova explosion or an outburst from a second supermassive black hole near the galaxys center.

While they want to watch the objects future behavior to make sure, they pointed out that the object has remained too bright for too long to be consistent with any known type of supernova.

Because of this extraordinary brightness, we consider the supernova explanation unlikely, said Dr. Vivek Dhawan, an astronomer at the National Radio Astronomy Observatory.

While the new object definitely is separate from Cygnus As central supermassive black hole, by 1,500 light-years, it has many of the characteristics of a supermassive black hole that is rapidly feeding on surrounding material.

We think weve found a second supermassive black hole in this galaxy, indicating that it has merged with another galaxy in the astronomically-recent past, said Dr. Christopher Carilli, an astronomer at the National Radio Astronomy Observatory.

These two would be one of the closest pairs of supermassive black holes ever discovered, likely themselves to merge in the future.

The astronomers suggested that the second black hole has become visible to the VLA in recent years because it has encountered a new source of material to devour.

That material could either be gas disrupted by the galaxies merger or a star that passed close enough to the secondary black hole to be shredded by its powerful gravity.

The research paper reporting this discovery has been accepted for publication in the Astrophysical Journal (arXiv.org preprint).

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Daniel A. Perley et al. 2017. Discovery of a Luminous Radio Transient 460 pc from the Central Supermassive Black Hole in Cygnus A. ApJ, accepted for publication; arXiv: 1705.07901

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